PROJECT SUMMARY/ABSTRACT The long-term goal of this project is to elucidate the molecular determinants of the regulation of corneal epithelial cell phenotype. It is now apparent that corneal epithelial cell phenotype must be held in check by constant transcriptional maintenance, or it may suffer reprogramming to alternate epithelial fates. While many specific genetic and environmental causes can trigger this change, the final result is consistent and catastrophic for vision. In this current proposal I present plans to study the nuclear protein pinin (Pnn). Our recent data indicate that silencing of the gene for Pnn during development results in a loss of normal corneal epithelial features and the change to a keratinizing epithelium. These data have taken our studies to an exciting new direction involving the exploration of Pnn as a key regulator of specific epithelial identity. We now present plans to define the consequences of pnn deletion in the mature corneal epithelial integrity by constructing inducible knockouts. Using these animals, we wish to characterize the impact of pnn deletions on the limbal stem cell compartment. We will also explore the relationship of Pnn and Pax6 in the genetic regulation/reprogramming of cell fate differentiation decision of the corneal epithelium. Finally, we will elucidate the relationship of Pnn deletion to Wnt pathway activation and maintenance of epithelial cell identity, by investigating beta-catenin activation and the involvement of a Pnn-partner, RNA helicase p68, in this process. The three proposed aims address fundamental issues of corneal epithelial biology and will provide a new window into the molecular processes by which epithelial identity is established and maintained by the corneal epithelium. Studies addressing how the corneal epithelial identity is established and maintained are central to vision research and resolving these molecular details and pathways pertaining to these processes will contribute significantly to the design of new therapies to impact the maintenance and repair of the corneal epithelial phenotype and the corneal epithelium physiology and barrier.